In our daily lives, drinking water is essential for human to maintain function of body. However, after the drinking water is in contact with air for a period of time, bacteria in the drinking water is contaminated and increased. Therefore, when user drinks the drinking water with increased bacteria, discomfort can easily occur to the user.
A known drinking water purifying method is to add an ultraviolet source at a cover of a cup or a bottle. When the cover of cup or bottle is covered on a water bottle or a water cup, the ultraviolet source generates an ultraviolet to the drinking water in the water bottle or water cup to kill bacteria. However, when the cover of cup or bottle is not covered on the water bottle or water cup, the ultraviolet generated by the ultraviolet source is likely to be emitted to human body and cause harm. In addition, the cover of cup or bottle provided with the ultraviolet source is only adapted for the water bottle or water cup with corresponding size but not adapted for the water bottle or water cup of various sizes.